1. Field Of The Invention
The present invention relates to single lens reflex (SLR) cameras and more particularly to means for improving the compactness of SLR cameras with zoom lenses.
2. Description Relative To The Prior Art
Single lens reflex (SLR) cameras have obvious advantages as compared to other types of conventional cameras, the most important advantage being the ability to view the object precisely as it will be imaged on the film, regardless of the lens focal length or the object distance. This is accomplished by placing a viewfinder mirror in the ray path of the taking lens close to the film plane to allow the object to be imaged by the objective lens on a focusing screen that is viewed through the optical system of the viewfinder. The mirror may be removed from the taking lens ray path during the film exposure, but always assumes the same position during viewfinding.
Almost all SLR cameras are designed to accept interchangeable lenses, the most versatile of which is a so-called macro-zoom lens, which provides for a continuous range of different focal lengths and for focusing on objects from infinity to relatively close to the camera. For example a 35 mm camera equipped with a macro-zoom lens with a focal length range of 30-105 mm (i.e. a 31/2 to 1 zoom ratio) and the ability to focus objects as close as 0.5 mm to the camera (i.e. macro focus) could be considered as representative of a general purpose camera that would meet all of the requirements of most amateur photographers. However, because of optical design considerations related to the location of the mirror, which dictates a long back-focal length, a zoom, and particularly a macro-zoom lens is necessarily quite large, both in length and also in the diameter of the frontal optical elements. Also, the mirror requires that the rearward element of the relatively long lens be at a considerable distance from the film plane, which further increases the overall length of the camera. Furthermore, a conventional SLR camera is necessarily quite large in its vertical dimension because of the location of the viewfinder penta prism above the film path. Consequently, a SLR camera with such a lens feature is entirely too large to be acceptable for general purpose amateur use without the expensive and inconvenient option of interchangeable conventional lenses to allow it to be made more compact.